First you'll need to connect your PC to nRF52-DK via USB-micro cable, then you'll need to connect the nRF52-DK to Ruuvi via devkit or the Tag-Connect cable. nRF52-DK autodetects an external target and programs it, but if there is an issue with connection you can get errors from the software or program the nRF52 onboard the nRF52-DK. You can cut the power measurement jumper on nRF52-DK to be sure to not accidentally connect to the wrong nRF52.